• Created by: Aisham36
  • Created on: 29-09-15 19:45


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What is Respiration?

Respiration is not the same thing as breathing. That is more properly called ventilation. Instead, respiration is a chemical process in which energy is released from food substances, such as glucose - a sugar.

It is the chemical process of breaking down glucose to release energy and happens in every cell belonging to living things. It is how they get energy from their food.

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Breathing System


Oxygen is inhaled into the body and diffused through the alveoli into the red blood cells. Carbon dioxide is excreted through the alveoli.

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The Digestive System

Enzymes break down carbohydrates into small glucose molecules which are transported around the body in the circulatory system.

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The Circulatory System

Image result for the circulatory system

This system transports oxygen and glucose to different organs to carry out respiration.

It is important to note that oxygenated blood is transported in arteries away from the heart and deoxygenated blood is transported to the heart in veins.

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Exercise and Respiration (key terms)

Anaerobic respiration = Respiration without oxygen! Glucose is broken down to form lactic acid, water and a small amount of energy. Sprinters run off their anaerobic system.

Muscle Fatigue = Muscles become fatigued after long periods of use. This means they stop contracting efficiently. At this stage they are short of oxygen and respire anaerobically.

Lactic Acid = Lactic acid is a product of anaerobic respiration. Glucose is broken down into lactic acid and ATP (energy.) Lactic acid builds up in the muscles.

Oxygen Debt = The additional oxygen that must be taken into the body after vigorous exercise to return all systems to a normal rate.

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Aerobic Respiration

Aerobic respiration needs oxygen to work. Most of the chemical reactions involved in the process happen in tiny objects inside the cell cytoplasm, called mitochondria.

This is the equation for aerobic respiration:

glucose + oxygen → carbon dioxide + water (+ energy)

6CO2 + C6H12O6  -> 6H2O + 6CO(+ energy)

The energy released by respiration is used to make large molecules from smaller ones. In plants, for example, sugars, nitrates and other nutrients are converted into amino acids. Amino acids can then join together to make proteins. The energy is also used:

  • To allow muscles to contract in animals
  • To maintain a constant body temperature in birds and mammals

When there is too much glucose within the body, it is converted into glycogen which is stored in the muscles and is converted back into glucose when the body is exercising.  

During exercise the oxygen content decreases and the carbon dioxide content increases.

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Anaerobic Respiration

 Glucose -> Lactic Acid + Energy

Anaerobic respiration occurs when there is a short supply of oxygen. It allows the body to release energy in some cells when no oxygen is available. Lactic acid is toxic and damages muscles (muscle fatigue) if it is not removed quickly. Lactic acid causes pain and cramps.

 Anaerobic respiration involves the incomplete breakdown of glucose. It releases around 5% of the energy released by aerobic respiration, per molecule of glucose

Oxygen debt

This is the amount of oxygen needed to oxidise lactic acid to carbon dioxide and water. The existence of an oxygen debt explains why we continue to breathe deeply and quickly for a while after exercise.

The recovery period is when our body brings back oxygen concentrations to normal.

Glucose -> lactic acid + energy + oxygen -> carbon dioxide + water

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